Water-dispersing coated shaped bodies

ABSTRACT

A process for the production of coated planar moldings of thermoplastics is disclosed. The process entails extrusion of a molded body, cooling of the molding, applying the aqueous-based coating agent and drying. The coating agent, having a pH value of less than 6, contains a salt of sulfondicarboxylic diester, a water-insoluble oxide of metal or semi-metal and an acid/water mixture. It is applied to at least one surface of the molding immediately after the production of the molding and with the aid of an application roll.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

The present patent application claims the right of priority under 35U.S.C. §119 (a)-(d) and 35 U.S.C. §365 of International Application No.PCT/EP99/04181, filed Jun. 17, 1999, which was published in German asInternational Patent Publication No. WO 00/00297 on Jan. 6, 2000, whichis entitled to the right of priority of German Patent ApplicationNumbers 198 29 082.9 and 198 29 081.0 each filed on Jun. 30, 1998.

FIELD OF THE INVENTION

The present invention relates to planar mouldings consisting ofthermoplastics and provided with a water-spreading coating, to twoprocesses for their production and also to their use.

BACKGROUND OF THE INVENTION

The term “water-spreading” is to be understood to mean the property of asurface for forming a contact angle of below 20 degrees with a drop ofwater applied on it. A water-spreading coating is accordingly a coatingthat brings about this property of a surface.

Mouldings with a water-spreading surface have the property that waterwhich gets onto their surface is not concentrated there into drops whichare separate from one another but rather that the drops spread out and,when they come into contact, run together to form a closed layer. As aresult, an improved reflection of light on the surface that is moistenedwith water and a better transmission of light in the case of transparentmouldings are achieved. In addition, the dripping of water from theunderside of the moulding is rendered difficult. These so-calledanti-drop properties which impede the formation of drops are demanded,in particular, for various glazing materials consisting ofthermoplastics. In such cases it is desired that condensed water orcondensate water deposited thereon does not fall off in the form ofdrops but rather that it runs off, following the downward gradient ofthe material, in a closed layer or at least in coherent paths on thelower edge.

Behaviour contrary to that of a water-spreading surface is displayed bythe water-repellent surface. On water-repellent surfaces, water whichgets onto such a surface is concentrated into drops that are separatefrom one another.

Numerous attempts to provide water-repellent surfaces of plastics withwater-spreading layers are known from the literature. According to DE-A21 61 645, coatings of this type are produced from a mixed polymerconsisting of alkyl esters; hydroxyalkyl esters and quaternaryaminoalkyl esters of acrylic or methacrylic acid and methylol ethers ofmethacrylamide by way of crosslinking agent. They firstly take up water,subject to swelling, and gradually pass over into a water-spreadingstate. However, as a consequence of the swelling the coating becomessoft and sensitive to mechanical damage.

With a view to improving the mechanical strength of water-spreadingcoatings, inorganic constituents such as colloidal metal oxides, inparticular aluminium oxide, or colloidal silicon dioxide have beenworked into the coating compositions (EP-A 7 681 877 or EP-A 7 606 193).

In order to achieve higher mechanical stability, coatings withhydrophilic inorganic constituents in a hydrophilic binding agent havebeen developed. According to JP-A 76 81 877, polyvinyl-chloride films orpolymethyl-methacrylate films are covered with a coating consisting ofcolloidal aluminium oxide by way of hydrophilising, hard constituent andpolyvinyl alcohol and ammonium polyacrylate by way of binding agent.However, in the state swollen with water this coating is also sensitiveto mechanical loads.

There have also already been attempts to work wetting-friendly agentsinto the plastic material itself from which the moulding is produced.For instance, water-spreading coverings for greenhouses and similar damprooms are produced, according to DE-A 2 017 002, from a plastic thatcontains surface-active agents such as polyalkylene glycol. Thewater-spreading effect of this additive is not adequate. The resistanceof the plastic to weathering is also impaired.

In JP-A 76 06 193 polymethacrylate sheets with a coating consisting of95 parts of colloidal silicon dioxide and 5 parts of a dispersion of ahydrophobic acrylic resin are proposed as glazing means. However, theadhesion of this coating is totally unsatisfactory. This is true, aboveall, with respect to the moist state.

A better adhesion of a water-spreading coating on plastic mouldings isachieved, according to EP-A 51 405, with a covering synthesised from twolayers, both layers containing colloidal silicon dioxide, a partiallyhydrolysed polysiloxane and polyvinyl alcohol by way of binding agent.The ratio of silicon to carbon is greater in the lower layer than in theouter layer.

Generalising, it is possible to note that although a coating having agood water-spreading property can usually be achieved with stronglyhydrophilic covering materials, as a rule the coating is too soft in theswollen state. If it is desired to counteract this disadvantage by meansof a stronger crosslinking or less hydrophilicity, then thewater-spreading effect declines simultaneously with the mechanicalsensitivity. Although silicon dioxide and various other oxides of metalsor semimetals combine the advantages of great hardness and goodwettability by means of water without swelling, they have thedisadvantage that they do not adhere at all.

To the extent that use is made of binding agents with a view toanchoring the oxides on the surface of the plastic, the wettability ofthe oxides and hence the water-spreading effect of the coating declines,and the disadvantages of the binding agents appear: mechanicalsensitivity in the case of hydrophilic binding agents, and insufficientspreading of water in the case of hydrophobic binding agents.

In DE-A 34 00 079 it was proposed to bind a water-spreading layerconsisting substantially completely of silicon dioxide or other metaloxides of colloidal particle size, which itself has an insufficientadhesive strength on the layer of plastic, onto the water-repellentsurface of a plastic moulding in firmly adhering manner by means of anadhesion-promoting layer of an organic polymer having polar groups thatis not soluble in water and that is substantially not swellable.

All the named coating agents have the disadvantage that they have to beapplied from organic solvents.

The processes for applying the coating agents mentioned in the state ofthe art onto mouldings consisting of thermoplastics are elaborate.

SUMMARY OF THE INVENTION

With respect to the state of the art that has been mentioned it wastherefore a matter of making available a rational coating process whichfollows the production of the mouldings immediately—i.e., on-line—andwith which it is preferably possible to apply an aqueous coating agenteven without providing a layer of adhesion promoter. In addition, auniform and smooth coating of the surface of the moulding is to beguaranteed. The object further underlying the present invention is tomake available planar mouldings consisting of thermoplastics andprovided with a water-spreading coating and also to make possibilitiesavailable for their use.

In accordance with the invention, this object is achieved by means of aprocess comprising:

(i) preparing a planar thermoplastic molding by means of extrusion;

(ii) cooling said planar thermoplastic molding;

(iii) applying an aqueous based coating composition onto at least oneside of the cooled planar thermoplastic molding, said coating beingapplied by means of an application roll immediately after production ofsaid planar thermoplastic molding; and

(iv) drying the applied coating on said planar thermoplastic molding,wherein said aqueous coating composition comprises,

A) 0.005 to 2 parts by weight of a compound represented by generalformula (1),

for which,

R¹ is a C₁-C₃₀ hydrocarbon radical,

R² is hydrogen or a C₁-C₈ hydrocarbon radical,

A is a single bond or a divalent C₁-C₃₀ hydrocarbon radical,

B is a single bond or a divalent C₁-C₃₀ hydrocarbon radical,

n is 1, 2, 3 or 4, and

M^(n+) is a cation having an n-fold positive charge,

B) 1 to 20 parts by weight of at least one water-insoluble oxide of ametal or of a semimetal,

C) 80 to 100 parts by weight of a mixture of an acid and water, morethan 90% of which consists of water,

provided that the pH of said aqueous coating composition is less than 6.

In an embodiment of the present invention, the application roll rotatescontrary to the direction of transport of the planar thermoplasticmolding that is to be coated (referred to herein as “process A”).

In accordance with the present invention, there are also provided planarmouldings consisting of thermoplastics and provided with awater-spreading coating that can be obtained in accordance with theabove described process, and their use as a constituent part ofautomobiles, greenhouses, swimming pools, stadia, railway stations,factory buildings, roof coverings, walls, lamp covers, architecturalglazings, light cupolas, visors, spectacles, graphics, advertisinghoardings, displays, packagings or of panes for means of locomotion ofall types.

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, with the aforementioned so-called on-line processaccording to the invention it is possible to achieve a particularlyuniform coating and an outstandingly even, coated surface on themoulding if the application roll, with the aid of which the aqueouscoating composition is applied on the surface of the mouldings, rotatescontrary to the direction of transport of the coated moulding.

Moreover, the object according to the invention is achieved through aprocess for producing planar mouldings consisting of thermoplastics andprovided with a water-spreading coating by extrusion, cooling of themouldings, application and drying of a coating agent onto the mouldings,characterised in that the coating agent is synthesised on an aqueousbasis and in that it is applied onto at least one side of the planarmoulding immediately after production thereof with the aid of a flutedapplication roll and is then dried (called “process B” for short in thefollowing) and also through the provision of the planar mouldingsconsisting of thermoplastics and provided with a water-spreading coatingthat can be obtained in accordance with this process and their use as aconstituent part of automobiles, greenhouses, swimming pools, stadia,railway stations, factory buildings, roof coverings, walls, lamp covers,architectural glazings, light cupolas, visors, spectacles, graphics,advertising hoardings, displays, packagings or of panes for means oflocomotion of all types.

Surprisingly, with the aforementioned so-called on-line processaccording to the invention it is possible to achieve a particularlyuniform coating and an outstandingly even, coated surface on themoulding if use is made of a fluted application roll by way ofapplication roll with the aid of which the aqueous coating compositionis applied on the surface of the moulding.

A fluted application roll in the sense of the present invention is anapplication roll that exhibits fine, rib-like elevations or depressionson its surface. The fluted application roll according to the inventionis preferably made of steel or rubber and has a diameter preferably from0.5 to 25 cm, in particularly preferred manner from 0.8 to 2 cm. Inparticularly preferred manner the roll consists of a high-grade-steelrod with a high-grade-steel spiral with uniform spacings. As such, aSpiral-Rakel (spiral doctor blade) available from BYK-Gardner GmbH,D-82534 Geretsried, Germany or a so-called “K-Stab” (K-rod) availablefrom Erichsen GmbH & Co.KG, D-58675 Hemer, Germany can be employed, forexample. Since, in accordance with the invention, the application rollpreferably has no drive of its own but is driven only by the continualmovement of the planar moulding to be coated, use of the coating is farless trouble-prone in comparison with known process know-how.

The application roll is loaded with the aqueous coating composition, forexample with the aid of a metering device, preferably a pump. Acollecting vessel is preferably located in the region where loading orapplication of the coating composition takes place, in which any surpluscoating composition accruing is collected and returned to the meteringdevice, so that the process according to the invention can be operatedvery economically and ecologically.

With the process by means of extrusion according to the invention,sheets, in particularly preferred manner cellular sheets, or film websare preferably produced by thermoplastic material, preferably plasticgranular material, being subjected to conventional shaping by extrusion.In this connection it has proved to be advantageous with the processaccording to the invention to cool down the mouldings after theextrusion to the application temperature of the aqueous coatingcomposition, preferably to 20 to 80° C., in particularly preferredmanner to 40 to 70° C.

With a view to coating it is advantageous that the moulding to be coatedruns on at a belt speed that permits the aqueous coating composition tobe applied in quantities from 3 to 15 g/m² on the surface of themoulding. After being coated, the moulding passes through a drying-zonein which the coating is dried preferably at room temperature to 80° C.,and subsequently through a hardening-zone in which the coating isannealed at 90 to 155° C., preferably at 120 to 150° C.

For the transport of the extruded mouldings the known devices such asconveyor belts with and without haul-off rollers may be employed. Dryingand annealing may likewise be effected with known devices, preferablywith the aid of hot air, infrared radiators or by indirect action ofheat.

After the coating of one surface of the planar moulding other surfacescan also be coated, for example by the moulding being turned andsubjected once again to a coating operation.

The coated mouldings are advantageously isolated after being coated tothe desired extent.

Suitable by way of coating agents for the process according to theinvention are, in particular, coating agents synthesised on an aqueousbasis containing

A) 0.005 to 2 parts by weight of a compound represented by the generalformula (1)

in which

R¹ is a hydrocarbon residue with 1 to 30 C atoms,

R² is hydrogen or a hydrocarbon residue with 1 to 6 C atoms,

A is a single bond or a divalent hydrocarbon residue with 1 to 30 Catoms,

B is a single bond or a divalent hydrocarbon residue with 1 to 30 Catoms,

n is 1, 2, 3 or 4 and

M^(n+) is a cation with a positive charge n,

B) 1 to 20 parts by weight of a water-insoluble oxide or of severalwater-insoluble oxides of a metal or semimetal,

C) 80 to 100 parts by weight of a mixture of an acid and water,consisting of more than 90% water,

with the proviso that the pH value of the coating agent is less than 6.

In the case of the compounds represented by the general formula (1),which are employed as Component A of the coating agent according to theinvention, it is a question of sulfondicarboxylic diesters. These areemployed either as free acid (i.e., n=1 and M^(n+)=H⁺) or as salts. Incase the salts are employed, these may be the salts of arbitrarycations. For example, mention may be made of: elemental cations, organicor inorganic molecular cations or organic or inorganic complex cations.Use may also be made of mixtures of various cations.

Preferred compounds according to the general formula (1) are compoundsrepresented by the general formula (2)

in which

R¹ is an aliphatic hydrocarbon residue with 1 to 30 C atoms,

A is a single bond or a divalent aliphatic hydrocarbon residue with 1 to3 C atoms,

B is a single bond or a divalent aliphatic hydrocarbon residue with 1 to3 C atoms,

n is 1 or 2 and

M^(n+) is a cation with a positive charge n.

Particularly preferred compounds according to the general formula (1)are compounds represented by the general formula (3)

in which

R¹ is an aliphatic hydrocarbon residue with 1 to 30 C atoms,

n is 1 or 2 and

M^(n+) is a cation with a positive charge n.

Amongst these, the alkali salts or the alkaline-earth salts or mixturesthereof are preferred. Alkali salts are quite particularly preferred. Byway of example, mention may be made of sulfosuccinic-bis-(2-ethylhexylester)-sodium salt.

The compounds represented by the general formula (1) can be produced byknown processes. Some of them are commercially available.

With a view to producing the coating agents, the compounds representedby the general formula (1) can be employed as pure substance or in theform of a solution in an arbitrary solvent or mixture of solvents. Theyare preferably employed in the form of a solution. For example, thecommercial product Dapro®U99 produced by the Daniel Products Company,Inc., New Jersey, USA may be employed. This product is a solution of 40g sulfosuccinic-bis-(2-ethylhexyl ester)-sodium salt in 43 g2-butoxyethanol, 4 g ethanol, 3 g water and 10 gpolyethylene-glycol/fatty-acid ester (a mixture based substantially onpolyethylene-glycol/oleic-acid ester, polyethylene-glycol/palmitic-acidester and polyethylene-glycol/stearic-acid ester).

In the case where the compound represented by the general formula (1) isemployed in the form of a solution with a view to producing the coatingagent according to the invention, this has the consequence that thecoating agent contains other substances over and above the threecomponents A, B and C mentioned, namely the solvents of the solution ofthe compound represented by the general formula (1). The solution of thecompound represented by the general formula (1) should preferably have aconcentration from 5 to 95 wt.-%, in particular 10 to 90% and, quiteparticularly preferred, 20 to 60%.

By way of water-insoluble oxides of a metal or semimetal according tothe invention, use is preferably made of oxides of elements pertainingto the 3rd or 4th main group or to the 2nd, 3rd, 4th, 5th, 6th, 7th or8th subgroup of the periodic table of the elements. By way of examples,mention may be made of: aluminium oxide, silicon dioxide, titaniumoxide, cerium oxide, zinc oxide, tin oxide, chromium oxide, indiumoxide, zirconium oxide and iron oxides as well as pigments, inparticular transparent pigments. The oxides according to the inventionmay contain small quantities of other elements as doping agents.

The use of oxides of a metal or semimetal pertaining to the 3rd or 4thmain group of the periodic table of the elements is particularlypreferred. By way of example, mention may be made of: aluminium oxide orsilicon oxide.

The use of oxides of a metal or semimetal from the 4th main group of theperiodic table of the elements is quite particularly preferred. Amongstthese, silicon dioxide is most preferred.

The oxides of a metal or semimetal according to the invention arepreferably used in the form of a sol—i.e., as an aqueous, colloidalsolution—which preferably has a concentration amounting to 10 to 50mass-% of the metal oxide and has particles which, on average,preferably have diameters measuring less than 5 μm.

The oxide particles in the sol according to the invention are preferablypresent with an average size of less than 200 nm, in particularlypreferred manner in the range from 5 to 100 nm. The particle size isascertained by means of an ultracentrifuge.

The mixture of an acid and water according to the invention consists ofmore than 90% water. It preferably consists of more than 95% water, inquite particularly preferred manner more than 98% water. It may containorganic or inorganic acids. Use is preferably made of weak acids. Weakacids are those acids which have a pK_(a) value of more than 2. Inparticularly preferred manner use is made of aliphatic carboxylic acids.In quite particularly preferred manner use is made of acetic acid.

The coating agent according to the invention contains 0.005 to 2 partsby weight, preferably 0.01 to 0.5 parts by weight and, particularlypreferred, 0.05 to 0.4 parts by weight, of Component A.

The coating agent according to the invention contains 1 to 20 parts byweight, preferably 2 to 20 parts by weight and, particularly preferred,3 to 8 parts by weight, of Component B.

The coating agent according to the invention has a pH value of less than6, preferably less than 5.

The coating agents according to the invention may optionally containother components such as, for example, surfactants and organic solventswith a view to better wetting of the substrate, as well as flow-controlagents or defoamers.

Production of the coating agents according to the invention ispreferably effected by producing the sol of the oxide of a metal orsemimetal that is employed in water or by diluting a commerciallyavailable sol with water to the desired concentration in the coatingagent according to the invention, subsequently, in advantageous manner,by adjusting a weakly acidic pH, for example by addition of acetic acid,and by adding the quantity of Component A of the coating agent accordingto the invention that is stipulated for the coating agent.

In advantageous manner the coating agent and optionally also the sol ofthe oxide of a metal or semimetal that is optionally employed isfiltered, so that the respective composition only contains particleswith a particle diameter of, preferably, less than 5 μm.

In order to achieve a sufficiently water-spreading and mechanicallystable coating of the originally water-repellent plastic mouldings, theaqueous coating compositions should be applied in quantities from 3 to15, preferably 6 to 12, g/m² of surface, in order that the annealedlayer exhibits a layer thickness of, preferably, 0.2 to 0.3 μm.

With the process according to the invention, in particular transparentmouldings consisting of polyacrylates, polymethyl methacrylates,polystyrene, polyvinyl chloride or polycarbonates can be permanentlyfinished with a water-spreading covering that is totally uniform andsmooth by employing the coating agents that have been listed. Themouldings that are finished with anti-drop properties in this way aresuitable, in particular, as a glass substitute of any type, preferablyfor roof coverings, walls, lamp covers, architectural glazes, lightcupolas, visors, spectacles, graphics, advertising hoardings, displays,packagings and also panes for means of locomotion of all types.

Thermoplastics suitable for coating are described, for example, inBecker/Braun, Kunststoff-Handbuch, Carl Hanser Verlag, Munich, Vienna.The plastics may contain additives.

According to the invention it is possible, in particular, for anypolycarbonate to be coated.

Polycarbonates that are suitable in accordance with the invention areboth homopolycarbonates and copolycarbonates. A mixture of thepolycarbonates that are suitable in accordance with the invention canalso be used.

The polycarbonates may be partially or totally replaced by aromaticpolyester carbonates.

The polycarbonates may also contain polysiloxane blocks. The productionthereof is described in, for example, U.S. Pat. Nos. 3,821,315,3,189,662 and 3,832,419.

Preferred polycarbonates are those based on bisphenols of the generalformula (4)

HO—Z—OH  (4)

in which Z is a divalent organic residue with 6 to 30 C atoms thatcontains one or more aromatic groups.

Examples of bisphenols according to the general formula (4) arebisphenols that pertain to the following groups:

dihydroxydiphenyls,

bis-(hydroxyphenyl)-alkanes,

bis-(hydroxyphenyl)-cycloalkanes,

bis-(hydroxyphenyl)-sulfides,

bis-(hydroxyphenyl)-ethers,

bis-(hydroxyphenyl)-ketones,

bis-(hydroxyphenyl)-sulfones,

bis-(hydroxyphenyl)-sulfoxides and

α,α′-bis-(hydroxyphenyl)-diisopropylbenzenes.

Derivatives of the named bisphenols, which are available, for example,as a result of alkylation or halogenation on the aromatic rings of thenamed bisphenols, are also examples of bisphenols according to thegeneral formula (4).

Examples of bisphenols according to the general formula (4) are, inparticular, the following compounds:

hydroquinone,

resorcinol,

4,4′-dihydroxydiphenyl,

bis-(3,5-dimethyl-4-hydroxyphenyl)-methane,

bis-(3,5-dimethyl-4-hydroxyphenyl)-sulfone,

1,1-bis-(3,5-dimethyl-4hydroxyphenyl)-p/m-diisopropylbenzene,

1,1-bis-(4-hydroxyphenyl)-1-phenylethane,

1,1-bis-(3,5-dimethyl-4-hydroxyphenyl)-cyclohexane,

1,1-bis-(4-hydroxyphenyl)-3-methylcyclohexane,

1,1-bis-(4-hydroxyphenyl)-3,3-dimethylcyclohexane,

1,1-bis-(4-hydroxyphenyl)-4-methylcyclohexane,

1,1-bis-(4-hydroxyphenyl)-cyclohexane,

1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,

2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane,

2,2-bis-(3-methyl-4-hydroxyphenyl)-propane,

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)-propane,

2,2-bis-(4-hydroxyphenyl)-propane (i.e., bisphenol A),

2,2-bis-(3-chloro-4hydroxyphenyl)-propane,

2,2-bis-(3,5-dibromo-4-hydroxyphenyl)-propane,

2,4-bis-(4-hydroxyphenyl)-2-methylbutane,

2,4-bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane,

α,α′-bis-(4-hydroxyphenyl)-o-diisopropylbenzene,

α,α′-bis-(4-hydroxyphenyl)-m-diisopropylbenzene (i.e., bisphenol M) and

α,α′-bis-(4-hydroxyphenyl)-p-diisopropylbenzene.

Particularly preferred polycarbonates are the homopolycarbonate based onbisphenol A, the homopolycarbonate based on1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and thecopolycarbonates based on bisphenol A and1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

The bisphenols according to the general formula (4) that have beendescribed may be produced in accordance with known processes, forexample from the corresponding phenols and ketones.

Processes for producing the named bisphenols are described in, forexample, the monograph by H. Schnell entitled “Chemistry and Physics ofPolycarbonates”, Polymer Reviews, Volume 9, pp 77-98, IntersciencePublishers, New York, London, Sydney, 1964 and in U.S. Pat. No.3,028,635, in U.S. Pat. No. 3,062,781, in U.S. Pat. No. 2,999,835, inU.S. Pat. No. 3,148,172, in U.S. Pat. No. 2,991,273, in U.S. Pat. No.3,271,367, in U.S. Pat. No. 4,982,014, in U.S. Pat. No. 2,999,846, inDE-A 1 570 703, in DE-A 2 063 050, in DE-A 2 036 052, in DE-A 2 211 956,in DE-A 3 832 396 and in FR-A 1 561 518, as well as in the Japanesepublished applications having application numbers 62039/1986, 62040/1986and 105550/1986.

The production of 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane isdescribed in, for example, U.S. Pat. No. 4,982,014.

Polycarbonates may be produced in accordance with known processes.Suitable processes for producing polycarbonates are, for example,production from bisphenols with phosgene in accordance with thephase-interface process or from bisphenols with phosgene in accordancewith the process in homogeneous phase, the so-called pyridine process,or from bisphenols with carbonic esters in accordance with the melttransesterification process. These production processes are describedin, for example, H. Schnell, “Chemistry and Physics of Polycarbonates”,Polymer Reviews, Volume 9, pp 31-76, Interscience Publishers, New York,London, Sydney, 1964. The production processes that have been mentionedare also described in D. Freitag, U. Grigo, P. R. Müller, H. Nouvertne,“Polycarbonates” in Encyclopedia of Polymer Science and Engineering,Volume 11, Second Edition, 1988, pages 648 to 718 and in U. Grigo, KKirchner and P. R. Müller, “Polycarbonate” in Becker/Braun,Kunststoff-Handbuch, Volume 3/1, Polycarbonate, Polyacetale, Polyester,Celluloseester, Carl Hanser Verlag Munich, Vienna 1992, pages 117 to299.

The melt transesterification process is described, in particular, in H.Schnell, “Chemistry and Physics of Polycarbonates”, Polymer Reviews,Volume 9, pp 44-51, Interscience Publishers, New York, London, Sydney,1964 and also in DE-A 1 031 512, in U.S. Pat. No. 3,022,272, in U.S.Pat. No. 5,340,905 and in U.S. Pat. No. 5,399,659.

Carbonic diesters that can be employed for producing polycarbonates inaccordance with the melt transesterification process are, for example,diaryl esters of carbonic acid, with the two aryl residues preferablyeach having 6 to 14 C atoms. The diesters of carbonic acid based onphenol or alkyl-substituted phenols—that is, for example, diphenylcarbonate or dicresyl carbonate—are preferably employed.

The polycarbonates that are suitable in accordance with the inventionpreferably have a weight-average molar mass ({overscore (M)}_(w)), whichcan be determined by, for example, ultracentrifugation or byscattered-light measurement, from 10,000 to 200,000 g/mole. Inparticularly preferred manner they have a weight-average molar mass from12,000 to 80,000 g/mole.

The mean molar mass of the polycarbonates according to the inventioncan, for example, be adjusted in known manner by means of an appropriatequantity of chain terminators.

Suitable chain terminators are both monophenols and monocarboxylicacids. Suitable monophenols are, for example, phenol, p-chlorophenol,p-tert.-butylphenol, cumylphenol or 2,4,6-tribromophenol, as well aslong-chain alkylphenols such as, for example,4-(1,1,3,3-tetramethylbutyl)-phenol or monoalkylphenols ordialkylphenols with a total of 8 to 20 C atoms in the alkylsubstituents, such as, for example 3,5-di-tert.-butylphenol,p-tert.-octylphenol, p-dodecylphenol, 2-(3,5-dimethylheptyl)-phenol or4-(3,5-dimethylheptyl)-phenol. Suitable monocarboxylic acids are benzoicacid, alkylbenzoic acids and halobenzoic acids.

Preferred chain terminators are phenol, p-tert.-butylphenol,4-(1,1,3,3-tetramethylbutyl)-phenol and cumylphenol.

The quantity of chain terminators preferably amounts to between 0.5 and10 mole-%, relative to the sum of the bisphenols employed in eachinstance.

The polycarbonates that are suitable in accordance with the inventionmay be branched in known manner and, to be specific, preferably throughthe incorporation of trifunctional branching agents or branching agentsof higher functionality. Suitable branching agents are, for example,those with three, or more than three, phenolic groups or those withthree, or more than three, carbonic-acid groups.

Suitable branching agents are, for example, phloroglucinol,4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptene-2,4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane,1,3,5-tri-(4-hydroxyphenyl)-benzene, 1,1,1-tri-(4-hydroxyphenyl)-ethane,tri-(4-hydroxyphenyl)-phenylmethane,2,2-bis-[4,4-bis-(4-hydroxyphenyl)-cyclohexyl]-propane,2,4-bis-(4-hydroxyphenylisopropyl)phenol,2,6-bis-(2-hydroxy-5′-methylbenzyl)-4-methylphenol,2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane,hexa-(4-(4-hydroxyphenylisopropyl)-phenyl)-terephthalic ester,tetra-(4-hydroxyphenyl)-methane,tetra-(4-(4-hydroxyphenylisopropyl)-phenoxy)-methane and1,4-bis-(4′,4″-dihydroxytriphenyl)-methylbenzene, as well as2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride,3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole, trimesictrichloride and α,α,α″-tris-(4-hydroxyphenol)-1,3,5-triisopropylbenzene.

Preferred branching agents are3,3-bis-(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole and1,1,1-tris-(4-hydroxyphenyl)-ethane.

The quantity of the branching agents to be optionally employedpreferably amounts to 0.05 mole-% to 2 mole-%, relative to moles ofbisphenols employed.

In the case where the polycarbonate is produced in accordance with thephase-interface process, the branching agents may, for example, besubmitted with the bisphenols and the chain terminators in the aqueousalkaline phase or may be added, dissolved in an organic solvent,together with the carbonic-acid derivatives. In the case of thetransesterification process, the branching agents are preferably meteredtogether with the dihydroxy aromatics or bisphenols.

With a view to modifying the properties, conventional additives may beadmixed to the polycarbonates according to the invention and/or appliedonto the surface of the mouldings. Conventional additives are, forexample: fillers, reinforcing substances, stabilisers (for example, UVstabilisers, thermal stabilisers, gamma-ray stabilisers), antistaticagents, flow aids, mould-release agents, fire-protection agents,dyestuffs and pigments. The named additives and other suitable additivesare described in, for example, Gächter, Müller, Kunststoff-Additive, 3rdEdition, Hanser-Verlag, Munich Vienna, 1989.

Other polymers may be admixed to the polycarbonates according to theinvention, as a result of which so-called polymer blends are obtained.For example, blends may be produced from the polycarbonates according tothe invention and polyolefins, in particular ABS polymers.

The invention is elucidated in more detail below in the followingexamples.

Production of the Coating Agents

Coating Agent A

To 416.7 g of completely desalinated water there are added, subject tostirring, 83.3 g silica sol (Levasil® 300F, produced by Bayer AG) whichhad previously been filtered through a 5 μm filter. The aqueoussuspension is then adjusted with 98-% acetic acid to a pH value of 4.8and is mixed with 1.5 g Dapro® U99 (a solution of 40 gsulfosuccinic-bis-(2-ethylhexyl ester)-sodium salt in 43 g2-butoxyethanol, 4 g ethanol, 3 g water and 10 gpolyethylene-glycol/fatty-acid ester (a mixture based substantially onpolyethylene-glycol/oleic-acid ester, polyethylene-glycol/palmitic-acidester and polyethylene-glycol/stearic-acid ester).

Levasil® 300F is an anionically stabilised silica sol produced by BayerAG having a mean particle size from 7 to 8 nm or a specific surface of300 m²/g. Levasil® 300F has a solids content of 30 mass-% and a pH valueof about 9.8. It contains a small quantity amounting to ≦0.2 wt.-% offormaldehyde in order to counter attack by micro-organisms.

Coating Agent B

Production is effected in a manner analogous to that for coating agentA. Instead of Dapro® U99, however, there are added 0.675 gsulfosuccinic-bis-(2-ethylhexyl ester)-sodium salt in 0.825 g2-butoxyethanol.

Coating Agent C

Production is effected in a manner analogous to that for coating agentA. Instead of the named solution, however, there are added 0.621 gsulfosuccinic-bis-(2-ethylhexyl ester)-sodium salt, 0.054 g polyethyleneglycol (number-average molar mass: 1,000) in 0.754 g 2-butoxyethanol and0.0705 g ethanol.

Coating Agent D

Production is effected in a manner analogous to that for coating agentC. Instead of the polyethylene glycol there are added 0.062 gpolyethylene-glycol/fatty-acid ester (a mixture based substantially onpolyethylene-glycol/oleic-acid ester, polyethylene-glycol/palmitic-acidester and polyethylene-glycol/stearic-acid ester).

Coating of Polycarbonate Cellular Sheets

Cellular sheets consisting of a branched aromatic polycarbonate(relative solution viscosity 1.315, measured in respect of a solution of0.5 g polycarbonate in 100 ml methylene chloride at room temperature),such as are used for the construction of greenhouses, were each coatedon one side with the coating agents A to D in a flow-coating process andsubsequently dried at 130° C. for 0.5 h. The layer thicknesses amountedto around 0.3 μm (thickness gauge ETA-SD-30 manufactured by ETA-Optik;interference method). The coatings had no surface faults and showed nointerference pattern. The wetting with water was uniform. The contactangle of the water was below 1°.

Steam Test (100° C.)

As a further test, the steam test was carried out. In this connectionthe cellular sheets were exposed to a sealed water-vapour atmosphere ata temperature of 100° C. An observation is made as to when thewater-spreading effect disappears and the first formation of dropsoccurs.

Result

Lifespan of the coating in the Coating agent steam test Example A over 3hours

Model-greenhouse Test

The coated polycarbonate cellular sheets were attached at an angle of60°, with the coated side down, to the ceiling of a model greenhouse, sothat the water-spreading effect could be compared by observing theformation of droplets. Water was evaporated in the model greenhouse bymeans of a heating source, so that a temperature of 50° C. and ahumidity of 100% set in.

The sheets were left for 6 h under these conditions and weresubsequently heated for 4 h in a dry heating cabinet at 40° C.Subsequently the procedure was repeated in the model greenhouse and inthe heating cabinet, always in alternating manner, for such time untilthe water-spreading effect disappeared (evident from the formation ofdrops on the sheet).

Result

Lifespan of the Coating coating (in cycles) Example 1 A >80 Example 2B >80 Example 3 C >80 Example 4 D >80 Example 5 copolyacrylate/silicasol >80 Example 6 polyvinylpyrrolidone/silica sol 15 Example 7surfactant/silica sol 15

Examples Relating to On-line Coating (According to “Process A”)

Granular, branched bisphenol A polycarbonate (relative solutionviscosity 1.315, measured in respect of a solution of 0.5 gpolycarbonate in 100 ml methylene chloride at room temperature) wasextruded to form cellular sheets having a thickness of 6 mm and aspecific weight of 1.3 kg/m² using a single-screw extruder at 290° C.After calibration, the aqueous coating having the composition accordingto Example 1 was applied with an Optiroller manufactured by Bürkle (rollcoater SAL), which possessed a rubberised reverse-running applicationroll having a hardness of 50 Shore, onto the cellular sheet. The speedof the roll amounted to 8 m/min with a roll thickness of 238 mm. Thequantity applied was regulated via a pump. After a short drying-distanceof 1.5 m, annealing of the coating was effected. The cellular sheet wasthen sawn up into individual sheets. The coated sheets exhibit a highdegree of brilliance in comparison with the original sheets and possessan excellent water-spreading property. The coating cannot be detached inthe adhesive-tape test (Tesafilm test). Even after 80 cycles, no changein the spreading of water was detected in the model greenhouse.

The results of a number of trials are listed below.

Application Quantity Annealing Appearance of Spreading Model-greenhouseExamples temperature (° C.) applied (g/m²) Type Time (min) Temp. (° C.)the sheets of water test (cycles) 8 RT 10 ambient air 4 120 highbrilliance very good >80 9 RT 7.2 ambient air 4 120 high brilliance verygood >80 10 RT 10 ambient air 4 94 high brilliance very good >80 11 RT10 infra red 2 138 high brilliance very good >80 RT = room temperature

Examples Relating to On-line Coating (According to “Process B”)

Granular, branched bisphenol A polycarbonate (relative solutionviscosity 1.315, measured in respect of a solution of 0.5 gpolycarbonate in 100 ml methylene chloride at room temperature) wasextruded to form cellular sheets having a thickness of 6 mm and aspecific weight of 1.3 kg/m² using a single-screw extruder at 290° C.After calibration, the aqueous coating having the composition accordingto Example 1 was applied with a metering pump and a tracking flutedsteel roll at 60° C. The quantity applied was regulated via a meteringpump. The application by pump was effected in planar manner immediatelyupstream of the roll. The thickness of the roll amounted to 10 mm.

After a drying-distance of about 50 cm, annealing of the coating waseffected for 4 minutes in a circulating-air stretch at a temperature ofup to 130° C. The cellular sheet was then sawn up into individualsheets. The coated sheets exhibit an improved brilliance in comparisonwith the original sheets and possess an excellent water-spreadingproperty. The coating cannot be detached in the adhesive-tape test(Tesafilm test). Even after 80 cycles, no change in the spreading ofwater was detected in the model greenhouse.

The results of a number of trials are listed below:

Concen- Model- tration Spread- green- of Number of Quantity Appearanceing house Exa- coating flutes per applied of the of test mple agent¹⁾inch (g/m²) sheets water (cycles) 12 5 16 7.4 good very >80 brilliancegood 13 5 16 4.6 good very >80 brilliance, good slightly iridescent 1410 16 4.6 good very >80 brilliance good 15 10 32 4.6 good very >80brilliance good ¹⁾“Concentration of the coating agent” means the contentof all substances in the coating agent that are not water, in % by mass.

What is claimed is:
 1. A process for producing a planar thermoplasticmolding having a water-spreading coating on at least one side of saidmolding, said process comprising: (i) preparing a planar thermoplasticmolding by means of extrusion; (ii) cooling said planar thermoplasticmolding; (iii) applying an aqueous based coating composition onto atleast one side of the cooled planar thermoplastic molding, said coatingbeing applied by means of an application roll immediately afterproduction of said planar thermoplastic molding; (iv) drying the appliedcoating on said planar thermoplastic molding at a temperature from roomtemperature to 80° C.; and (v) annealing the dried coating of step (iv)at a temperature of 90° C. to 155° C., wherein said aqueous coatingcomposition comprises, A) 0.005 to 2 parts by weight of a compoundrepresented by general formula (1),

for which, R¹ is a C₁-C₃₀ hydrocarbon radical, R² is hydrogen or a C₁-C₆hydrocarbon radical, A is a single bond or a divalent C₁-C₃₀ hydrocarbonradical, B is a single bond or a divalent C₁-C₃₀ hydrocarbon radical, nis 1, 2, 3 or 4, and M^(n+) is a cation having an n-fold positivecharge, B) 1 to 20 parts by weight of at least one water-insoluble oxideof a metal or of a semimetal, C) 80 to 100 parts by weight of a mixtureof an acid and water, more than 90% of which consists of water, providedthat the pH of said aqueous coating composition is less than
 6. 2. Theprocess of claim 1 wherein said planar thermoplastic molding is one of asheet and a film web.
 3. The process of claim 1 wherein said planarthermoplastic molding consists of a transparent thermoplastic.
 4. Theprocess of claim 1 wherein said planar thermoplastic molding consists ofpolycarbonate.
 5. The process of claim 1 wherein said aqueous coatingcomposition is applied in quantities from 3 to 15 g/m² onto the surfaceof said planar thermoplastic molding.
 6. The process of claim 1 whereinafter extrusion step (i) the planar thermoplastic molding is cooled instep (ii) to the temperature at which the aqueous coating composition isapplied in step (iii).
 7. The process of claim 6 wherein the planarthermoplastic molding is cooled to 20 to 80° C. in step (ii).
 8. Theprocess of claim 1 wherein said application roll is a fluted applicationroll.
 9. The process of claim 8 wherein said fluted application roll ismade of one of rubber and steel.
 10. The process of claim 1 wherein saidapplication roll is driven only by a continual movement of said planarthermoplastic molding.
 11. The process of claim 1 wherein saidapplication roll rotates contrary to the direction of transport of saidplanar thermoplastic molding.
 12. The thermoplastic molding, having awater-spreading coating on at least one side, prepared by the process ofclaim 1.